Engine nacelles are used to control input and exhaust of engine air flow, facilitate maintenance, and suppress noise generated by high bypass turbofan engines. A nacelle may include an acoustic liner made up of a composite sandwich structure of face sheets and a honeycomb core. The face sheets are perforated for noise attenuation. The nacelle may further include insulation blankets made of ceramic and metallic materials between the acoustic liner and the engine's core. The insulation blankets protect the sandwich structure against the engine heat.
The insulation blankets add weight, require maintenance, and increase the cost of the nacelle, but do not directly provide structural benefit. Moreover, the insulation blankets take up significant space that may cause fan duct diameter to increase. They also place a non-smooth surface in the path of large volumes of air flow, which increases drag. The increased aircraft weight and drag are detrimental to fuel efficiency.
A need exists for a high-temperature acoustic liner with noise attenuation capability. Due to the shape of a typical gas turbine engine and nacelle performance needs, a further need exists for the acoustic liner to conform to complex (e.g., double contoured) surfaces.